The use of intermediate shaft brakes in automatic stage-geared vehicle gearboxes having at least some non-synchromesh gear stages and an input shaft coupled by way of an automatic friction clutch to an output shaft of an engine is already known. With the aid of a control computer and the vehicle's throttle control, the clutch in a known embodiment is controlled in such a way that when the vehicle is stationary with the engine running, and a gear selector coupled to the control computer is in the neutral position, the clutch is engaged, which means that the intermediate shaft and hence also the gear wheels meshing with the intermediate shaft gear wheels are rotating.
When the vehicle is to start and the gear selector is set to a gear position for selecting the starting gear, the clutch is disengaged. The disengaged gear wheel on the main shaft, by way of which the torque is to be transmitted to the selected gear, must first be braked to a standstill before the gear wheel can be locked to the shaft. If the selected gear is a synchromesh gear, the braking is performed with the aid of associated synchromesh elements, but if the selected gear is a gear with no synchromesh element, the braking is achieved by way of the intermediate shaft being braked to a standstill by the intermediate shaft brake.
However, an intermediate shaft brake can also be used for synchronization, either alone or together with an engine speed adjustment, when shifting between different gears, especially when shifting up. The time taken from the initiation of a gear shift, either when engaging the starting gear or shifting between different gears, until the gear shift is completed is to a large extent influenced by the torque transmission characteristic of the intermediate shaft brake, which is in turn influenced by factors such as temperature, brake lining wear and application and release times.
Insufficient account has hitherto been taken of the variations in the torque characteristic of the intermediate shaft brake as a function of the aforementioned factors, and this has had an effect on the gearshift time. The effect of temperature and wear which results in reduced brake torque have meant that the synchronization sequence and hence the gearshift time have been prolonged.